Re: [PATCH] fortran: Enable target preprocessor macros with -cpp [PR42954]

"Albert, Christopher" <[email protected]>
Newsgroups gmane.comp.gcc.patches,gmane.comp.gcc.fortran
Message-ID <[email protected]> 
On Mon, 27 Apr 2026 at 20:48, Harald Anlauf wrote:
> Am 27.04.26 um 8:37 PM schrieb Andrew Pinski:
>> On Thu, Apr 16, 2026 at 10:18 AM Christopher Albert <[email protected]> wrote:
>>>
>>> The Fortran preprocessor has never defined target-specific macros such as
>>> __linux__, __unix__, __ELF__, __x86_64__, or __amd64__ that the C
>>> preprocessor provides.  This was caused by the TARGET_OS_CPP_BUILTINS,
>>> TARGET_OBJFMT_CPP_BUILTINS, and TARGET_CPU_CPP_BUILTINS hooks being
>>> disabled since 2008 (marked as "Pandora's Box") because several target
>>> config headers use C-family-only functions.
>>>
>>> Fix by providing Fortran-compatible local helpers for
>>> builtin_define_std, builtin_define_with_value, and
>>> builtin_define_with_int_value (which in the C frontend live in
>>> c-family/c-cppbuiltin.cc and use the C-family-only globals parse_in
>>> and flag_iso), plus wrapper macros for c_dialect_cxx, flag_iso, and
>>> other C-family identifiers referenced by target config headers.  This
>>> allows TARGET_OS_CPP_BUILTINS and TARGET_OBJFMT_CPP_BUILTINS to
>>> execute in the Fortran frontend.
>>>
>>> Unlike the C frontend default (flag_iso=0, GNU extensions mode), the
>>> Fortran wrapper sets flag_iso=1 to suppress user-namespace macros like
>>> bare "unix" and "linux" that would conflict with Fortran identifiers.
>>> Only the reserved-namespace forms (__unix__, __linux__, etc.) are
>>> defined.  Fortran has no -std=cNN equivalent to control this, so the
>>> conservative choice avoids silent identifier replacement.
>>>
>>> For TARGET_CPU_CPP_BUILTINS, which on most architectures expands to a
>>> function in a C-family-only object file (e.g., ix86_target_macros in
>>> i386-c.cc), provide an x86 implementation directly in fortran/cpp.cc
>>> that covers architecture identification and float-size macros.
>>> ISA feature macros (__SSE__, __AVX__, etc.) are not included; if
>>> needed, they could be factored out of i386-c.cc into a shared object.
>>>
>>> Remove the dead __attribute__((target(...))) block from
>>> gfortran.dg/gomp/declare-variant-10.f90: it was guarded by
>>> #if defined(__x86_64__) which was previously always false because
>>> gfortran never defined these macros, and gfortran does not support
>>> C-style __attribute__ syntax.
>>>
>>> Co-authored-by: Kai Tietz <[email protected]>
>>>
>>>          PR fortran/42954
>>>
>>> gcc/fortran/ChangeLog:
>>>
>>>          * cpp.cc (gfc_builtin_define_std): New helper mirroring
>>>          builtin_define_std from c-family/c-cppbuiltin.cc.
>>>          (gfc_builtin_define_with_value): New helper mirroring
>>>          builtin_define_with_value from c-family/c-cppbuiltin.cc.
>>>          (gfc_define_ix86_target_macros): New function providing x86 CPU
>>>          identification macros for the Fortran preprocessor.
>>>          (gfc_darwin_cpp_builtins): New function providing Darwin platform
>>>          macros.
>>>          (cpp_define_builtins): Remove Pandora's Box FIXME.  Add wrapper
>>>          macros for C-family functions and variables used in target config
>>>          headers.  Set flag_iso=1 to suppress bare-name macros.  Enable
>>>          TARGET_OS_CPP_BUILTINS and TARGET_OBJFMT_CPP_BUILTINS.  Call
>>>          gfc_define_ix86_target_macros on x86 targets.
>> 
>> THIS is all wrong and causes too many issues. Please revert this.
>
> I haven't pushed yet, so all should be fine.
>
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>>          * gfortran.dg/gomp/declare-variant-10.f90: Remove dead
>>>          __attribute__((target)) block that is now exposed by newly
>>>          defined target macros.
>>>          * gfortran.dg/pr42954-linux.f90: New test.
>>>          * gfortran.dg/pr42954-x86.f90: New test.
>>>
>>> Signed-off-by: Christopher Albert <[email protected]>
>>> ---
>>>   gcc/fortran/cpp.cc                            | 178 ++++++++++++++++--
>>>   .../gfortran.dg/gomp/declare-variant-10.f90   |   3 -
>>>   gcc/testsuite/gfortran.dg/pr42954-linux.f90   |  24 +++
>>>   gcc/testsuite/gfortran.dg/pr42954-x86.f90     |  10 +
>>>   4 files changed, 194 insertions(+), 21 deletions(-)
>>>   create mode 100644 gcc/testsuite/gfortran.dg/pr42954-linux.f90
>>>   create mode 100644 gcc/testsuite/gfortran.dg/pr42954-x86.f90
>>>
>>> diff --git a/gcc/fortran/cpp.cc b/gcc/fortran/cpp.cc
>>> index 6b5f136e4f3..ada1bc1a211 100644
>>> --- a/gcc/fortran/cpp.cc
>>> +++ b/gcc/fortran/cpp.cc
>>> @@ -157,6 +157,126 @@ void pp_dir_change (cpp_reader *, const char *);
>>>   static int dump_macro (cpp_reader *, cpp_hashnode *, void *);
>>>   static void dump_queued_macros (cpp_reader *);
>>>
>>> +/* Fortran-local helpers that mirror builtin_define_std,
>>> +   builtin_define_with_value, and builtin_define_with_int_value from
>>> +   c-family/c-cppbuiltin.cc.  Those functions use the C-family-only
>>> +   globals parse_in and flag_iso, so they cannot be called directly
>>> +   from the Fortran frontend.  */
>>> +
>>> +/* Given "unix", define __unix, __unix__, and (if DEFINE_USER) unix.  */
>>> +
>>> +static void
>>> +gfc_builtin_define_std (cpp_reader *pfile, const char *macro,
>>> +                       bool define_user)
>>> +{
>>> +  size_t len = strlen (macro);
>>> +  char *buff = (char *) alloca (len + 5);
>>> +  char *p = buff + 2;
>>> +  char *q = p + len;
>>> +
>>> +  memcpy (p, macro, len + 1);
>>> +  if (!(*p == '_' && (p[1] == '_' || ISUPPER (p[1]))))
>>> +    {
>>> +      if (*p != '_')
>>> +       *--p = '_';
>>> +      if (p[1] != '_')
>>> +       *--p = '_';
>>> +    }
>>> +  cpp_define (pfile, p);
>>> +
>>> +  if (p != buff + 2)
>>> +    {
>>> +      if (q[-1] != '_')
>>> +       *q++ = '_';
>>> +      if (q[-2] != '_')
>>> +       *q++ = '_';
>>> +      *q = '\0';
>>> +      cpp_define (pfile, p);
>>> +      if (define_user)
>>> +       cpp_define (pfile, macro);
>>> +    }
>>> +}
>>> +
>>> +/* Define MACRO to EXPANSION; if IS_STR, quote the expansion.  */
>>> +
>>> +static void
>>> +gfc_builtin_define_with_value (cpp_reader *pfile, const char *macro,
>>> +                              const char *expansion, int is_str)
>>> +{
>>> +  size_t mlen = strlen (macro);
>>> +  size_t elen = strlen (expansion);
>>> +  char *buf = (char *) alloca (mlen + elen + 4);
>>> +  if (is_str)
>>> +    sprintf (buf, "%s=\"%s\"", macro, expansion);
>>> +  else
>>> +    sprintf (buf, "%s=%s", macro, expansion);
>>> +  cpp_define (pfile, buf);
>>> +}
>>> +
>>> +/* Provide x86 CPU identification macros for the Fortran preprocessor.
>>> +   TARGET_CPU_CPP_BUILTINS() cannot be called directly because it expands
>>> +   to ix86_target_macros() in i386-c.cc, which is only linked into
>>> +   C-family frontends.  This covers architecture identification and
>>> +   float-size macros.  ISA feature macros (__SSE__, __AVX__, etc.) and
>>> +   arch/tune macros (__znver4__, __skylake__, etc.) from
>>> +   ix86_target_macros_internal() are not included; if needed, they could
>>> +   be factored out of i386-c.cc into a shared object.  */
>>> +
>>> +#ifdef TARGET_80387
>> 
>> Please DON'T add target defines directly to the front-end.
>> Please instead use a config file from the target instead. Like what is
>> done for d, rust, etc. front-ends.
>> Each target should have their a source file which does the cpp_
>> instead of inlining it in the fortran front-end.
>> 
>> Thanks,
>> Andrea
>
> Alright, back to Chris...
>
> Thanks for stepping in quickly!
>
> Harald
>
>>> +static void
>>> +gfc_define_ix86_target_macros (cpp_reader *pfile)
>>> +{
>>> +  if (TARGET_64BIT)
>>> +    {
>>> +      cpp_assert (pfile, "cpu=x86_64");
>>> +      cpp_assert (pfile, "machine=x86_64");
>>> +      cpp_define (pfile, "__amd64");
>>> +      cpp_define (pfile, "__amd64__");
>>> +      cpp_define (pfile, "__x86_64");
>>> +      cpp_define (pfile, "__x86_64__");
>>> +      if (TARGET_X32)
>>> +       {
>>> +         cpp_define (pfile, "_ILP32");
>>> +         cpp_define (pfile, "__ILP32__");
>>> +       }
>>> +    }
>>> +  else
>>> +    {
>>> +      cpp_assert (pfile, "cpu=i386");
>>> +      cpp_assert (pfile, "machine=i386");
>>> +      gfc_builtin_define_std (pfile, "i386", false);
>>> +      cpp_define (pfile, "_ILP32");
>>> +      cpp_define (pfile, "__ILP32__");
>>> +    }
>>> +
>>> +  if (!TARGET_80387)
>>> +    cpp_define (pfile, "_SOFT_FLOAT");
>>> +
>>> +  if (TARGET_LONG_DOUBLE_64)
>>> +    cpp_define (pfile, "__LONG_DOUBLE_64__");
>>> +
>>> +  if (TARGET_LONG_DOUBLE_128)
>>> +    cpp_define (pfile, "__LONG_DOUBLE_128__");
>>> +
>>> +  cpp_define_formatted (pfile, "__SIZEOF_FLOAT80__=%d",
>>> +                       GET_MODE_SIZE (XFmode));
>>> +  cpp_define (pfile, "__SIZEOF_FLOAT128__=16");
>>> +}
>>> +#endif
>>> +
>>> +/* Provide essential Darwin platform macros for the Fortran preprocessor.
>>> +   The full darwin_cpp_builtins() in darwin-c.cc also defines
>>> +   __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ and
>>> +   __CONSTANT_CFSTRINGS__, but those depend on functions only linked
>>> +   into C-family frontends.  */
>>> +
>>> +static void ATTRIBUTE_UNUSED
>>> +gfc_darwin_cpp_builtins (cpp_reader *pfile)
>>> +{
>>> +  cpp_define (pfile, "__MACH__");
>>> +  cpp_define (pfile, "__APPLE__");
>>> +  gfc_builtin_define_with_value (pfile, "__APPLE_CC__", "1", false);
>>> +}
>>>
>>>   static void
>>>   cpp_define_builtins (cpp_reader *pfile)
>>> @@ -177,33 +297,55 @@ cpp_define_builtins (cpp_reader *pfile)
>>>     if (flag_openmp)
>>>       cpp_define (pfile, "_OPENMP=202111");
>>>
>>> -  /* The defines below are necessary for the TARGET_* macros.
>>> -
>>> -     FIXME:  Note that builtin_define_std() actually is a function
>>> -     in c-cppbuiltin.cc which uses flags undefined for Fortran.
>>> -     Let's skip this for now. If needed, one needs to look into it
>>> -     once more.  */
>>> +  /* Wrapper macros for C-family identifiers used in target config
>>> +     headers.  These allow TARGET_OS_CPP_BUILTINS and
>>> +     TARGET_OBJFMT_CPP_BUILTINS to compile in the Fortran frontend.  */
>>>
>>>   # define builtin_define(TXT) cpp_define (pfile, TXT)
>>> -# define builtin_define_std(TXT)
>>> +# define builtin_define_std(TXT) gfc_builtin_define_std (pfile, TXT, !flag_iso)
>>> +# define builtin_define_with_value(MACRO, EXPANSION, IS_STR) \
>>> +  gfc_builtin_define_with_value (pfile, MACRO, EXPANSION, IS_STR)
>>> +# define builtin_define_with_int_value(MACRO, VALUE) \
>>> +  cpp_define_formatted (pfile, "%s=" HOST_WIDE_INT_PRINT_DEC, \
>>> +                       MACRO, (HOST_WIDE_INT) (VALUE))
>>>   # define builtin_assert(TXT) cpp_assert (pfile, TXT)
>>> +# define c_dialect_cxx() 0
>>> +# define c_dialect_objc() 0
>>> +# define preprocessing_asm_p() 0
>>> +# define preprocessing_trad_p() 0
>>> +  /* Fortran has no -std=cNN flag to control this.  Set to 1 (ISO mode)
>>> +     so that builtin_define_std() only defines reserved-namespace macros
>>> +     like __unix__ and __linux__, not bare "unix" or "linux" which are
>>> +     valid Fortran identifiers and would cause silent replacement.  */
>>> +# define flag_iso 1
>>> +# define flag_isoc94 0
>>> +# define flag_isoc99 0
>>> +# define flag_isoc11 0
>>> +# define flag_isoc23 0
>>> +# define darwin_cpp_builtins(PFILE) gfc_darwin_cpp_builtins (PFILE)
>>>
>>> -  /* FIXME: Pandora's Box
>>> -    Using the macros below results in multiple breakages:
>>> -     - mingw will fail to compile this file as dependent macros
>>> -       assume to be used in c-cppbuiltin.cc only. Further, they use
>>> -       flags only valid/defined in C (same as noted above).
>>> -       [config/i386/mingw32.h, config/i386/cygming.h]
>>> -     - other platforms (not as popular) break similarly
>>> -       [grep for 'builtin_define_with_int_value' in gcc/config/]
>>> -
>>> -  TARGET_CPU_CPP_BUILTINS ();
>>>     TARGET_OS_CPP_BUILTINS ();
>>> -  TARGET_OBJFMT_CPP_BUILTINS (); */
>>> +  TARGET_OBJFMT_CPP_BUILTINS ();
>>> +
>>> +#ifdef TARGET_80387
>>> +  gfc_define_ix86_target_macros (pfile);
>>> +#endif
>>>
>>>   #undef builtin_define
>>>   #undef builtin_define_std
>>> +#undef builtin_define_with_value
>>> +#undef builtin_define_with_int_value
>>>   #undef builtin_assert
>>> +#undef c_dialect_cxx
>>> +#undef c_dialect_objc
>>> +#undef preprocessing_asm_p
>>> +#undef preprocessing_trad_p
>>> +#undef flag_iso
>>> +#undef flag_isoc94
>>> +#undef flag_isoc99
>>> +#undef flag_isoc11
>>> +#undef flag_isoc23
>>> +#undef darwin_cpp_builtins
>>>   }
>>>
>>>   bool
>>> diff --git a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90 b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
>>> index 0e0ab518010..115195e1194 100644
>>> --- a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
>>> +++ b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
>>> @@ -64,9 +64,6 @@ contains
>>>       call f18 ()          ! { dg-final { scan-tree-dump-times "f18 \\\(\\\);" 1 "gimple" } } */
>>>     end subroutine
>>>
>>> -#if defined(__i386__) || defined(__x86_64__)
>>> -  __attribute__((target ("avx512f,avx512bw")))
>>> -#endif
>>>     subroutine test2 ()
>>>       !$omp target
>>>         call f04 () ! { dg-final { scan-tree-dump-times "f03 \\\(\\\);" 1 "gimple" { target { { i?86-*-* x86_64-*-* } && { ! ilp32 } } } } }
>>> diff --git a/gcc/testsuite/gfortran.dg/pr42954-linux.f90 b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
>>> new file mode 100644
>>> index 00000000000..bd5efe7a237
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
>>> @@ -0,0 +1,24 @@
>>> +! { dg-do preprocess { target *-*-linux* } }
>>> +! { dg-options "-cpp" }
>>> +!
>>> +! PR fortran/42954 - target macros missing in gfortran -cpp
>>> +
>>> +#ifndef __linux__
>>> +# error __linux__ not defined
>>> +#endif
>>> +
>>> +#ifndef __linux
>>> +# error __linux not defined
>>> +#endif
>>> +
>>> +#ifndef __unix__
>>> +# error __unix__ not defined
>>> +#endif
>>> +
>>> +#ifndef __unix
>>> +# error __unix not defined
>>> +#endif
>>> +
>>> +#ifndef __ELF__
>>> +# error __ELF__ not defined
>>> +#endif
>>> diff --git a/gcc/testsuite/gfortran.dg/pr42954-x86.f90 b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
>>> new file mode 100644
>>> index 00000000000..0a3b7eac8a2
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
>>> @@ -0,0 +1,10 @@
>>> +! { dg-do preprocess { target { i?86-*-* x86_64-*-* } } }
>>> +! { dg-options "-cpp" }
>>> +!
>>> +! PR fortran/42954 - target macros missing in gfortran -cpp
>>> +
>>> +#if !defined(__i386__) && !defined(__i386) \
>>> +    && !defined(__x86_64__) && !defined(__x86_64) \
>>> +    && !defined(__amd64__) && !defined(__amd64)
>>> +# error x86 target macros not defined
>>> +#endif
>>> --
>>> 2.53.0
>>>
>>

Dear Andrea,

thanks for checking this.

I tried to keep the first version inside the Fortran frontend and overlooked the D/Rust frontend pattern you pointed out. I attached a smaller patch that adds a Fortran target hook and keeps the target-specific macro definitions in target config files.

Could you check whether this structure looks right? If yes, I can extend it toward the fuller scope Harald asked for in the Bugzilla thread.

Thanks,
Chris
0001-fortran-add-target-hook-for-Fortran-preprocessor-mac.patch (application/octet-stream, 33 KB) 
From a81f949a9a61a47f1c6f13240c28330c4310f5fc Mon Sep 17 00:00:00 2001
From: Christopher Albert <[email protected]>
Date: Tue, 28 Apr 2026 06:46:07 +0200
Subject: [PATCH] fortran: add target hook for Fortran preprocessor macros
 [PR42954]

gfortran -E -dM has emitted no target-identification macros since 2008
because gcc/fortran/cpp.cc disabled TARGET_CPU_CPP_BUILTINS,
TARGET_OS_CPP_BUILTINS, and TARGET_OBJFMT_CPP_BUILTINS.  Those target
macros expand into C-family-only state on many targets, so calling them
from the Fortran front end is not safe.

Add a small Fortran target hook vector and call one hook from the Fortran
preprocessor.  This keeps target-specific code out of gcc/fortran/cpp.cc
and gives target maintainers a place to add Fortran-safe macros without
using C-family helpers such as builtin_define_std.

This first patch intentionally implements only a viable scaffold:
Linux targets define the common Linux, Unix, and ELF reserved-namespace
macros, and x86 targets add the basic architecture and float-size macros.
Bare names such as linux and unix are not defined because they are valid
Fortran identifiers.  CPU feature macros, non-x86 CPU hooks, and other
operating systems are left for follow-up patches.

The now-reachable __attribute__((target)) block in
gomp/declare-variant-10.f90 is removed because gfortran has no
__attribute__ syntax; it was previously compiled out only because
__i386__ and __x86_64__ were never defined by gfortran.

Assisted-by: Claude (Anthropic)

	PR fortran/42954

gcc/ChangeLog:

	* Makefile.in (tm_f_file_list, tm_f_include_list): New
	substitution variables.
	(F_TARGET_DEF, F_TARGET_H): New.
	(TM_F_H): New.
	(tm_f.h, cs-tm_f.h): New rules.
	(fortran/f-target-hooks-def.h, s-f-target-hooks-def-h): New rules.
	(default-f.o): New rule.
	(generated_files): Add $(TM_F_H) and fortran/f-target-hooks-def.h.
	(s-tm-texi): Recognize fortran/f-target.def as a hook source.
	(build/genhooks.o): Depend on $(F_TARGET_DEF).
	* configure.ac: Compute tm_f_file_list and tm_f_include_list from
	$tm_f_file; substitute both.
	* configure: Regenerate.
	* config.gcc (target_has_targetfm): Document and initialize.
	(tm_f_file): New.
	(fortran_target_objs): Add per-target Fortran objects, linux-f.o on
	Linux targets, and default-f.o otherwise.
	* config/default-f.cc: New file.
	* config/i386/i386-f.cc: New file.
	* config/i386/i386-f.h: New file.
	* config/i386/t-i386 (i386-f.o): New rule.
	* config/linux-f.cc: New file.
	* config/t-linux (linux-f.o): New rule.
	* doc/tm.texi.in (Fortran ABI parameters): Add
	TARGET_F_CPP_BUILTINS.
	* doc/tm.texi: Regenerate.
	* genhooks.cc: Include fortran/f-target.def.
	* hooks.cc (hook_void_cpp_reader): New function.
	* hooks.h (hook_void_cpp_reader): Declare.

gcc/fortran/ChangeLog:

	* cpp.cc: Include tm_f.h and fortran/f-target.h.  Drop the local
	TARGET_CPU_CPP_BUILTINS, TARGET_OS_CPP_BUILTINS,
	TARGET_OBJFMT_CPP_BUILTINS, builtin_define, builtin_define_std, and
	builtin_assert fallback macros.
	(cpp_define_builtins): Call targetfm.f_cpp_builtins.
	* f-target-def.h: New file.
	* f-target.def: New file.
	* f-target.h: New file.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/declare-variant-10.f90: Drop dead
	__attribute__((target)) block.
	* gfortran.dg/pr42954-linux.f90: New test.
	* gfortran.dg/pr42954-x86.f90: New test.

Signed-off-by: Christopher Albert <[email protected]>
---
 gcc/Makefile.in                               | 31 +++++++-
 gcc/config.gcc                                | 20 +++++
 gcc/config/default-f.cc                       | 28 +++++++
 gcc/config/i386/i386-f.cc                     | 78 +++++++++++++++++++
 gcc/config/i386/i386-f.h                      | 25 ++++++
 gcc/config/i386/t-i386                        |  4 +
 gcc/config/linux-f.cc                         | 56 +++++++++++++
 gcc/config/t-linux                            |  4 +
 gcc/configure                                 | 19 ++++-
 gcc/configure.ac                              | 13 ++++
 gcc/doc/tm.texi                               | 14 ++++
 gcc/doc/tm.texi.in                            |  7 ++
 gcc/fortran/cpp.cc                            | 45 ++---------
 gcc/fortran/f-target-def.h                    | 20 +++++
 gcc/fortran/f-target.def                      | 44 +++++++++++
 gcc/fortran/f-target.h                        | 32 ++++++++
 gcc/genhooks.cc                               |  1 +
 gcc/hooks.cc                                  |  5 ++
 gcc/hooks.h                                   |  1 +
 .../gfortran.dg/gomp/declare-variant-10.f90   |  3 -
 gcc/testsuite/gfortran.dg/pr42954-linux.f90   | 33 ++++++++
 gcc/testsuite/gfortran.dg/pr42954-x86.f90     | 11 +++
 22 files changed, 449 insertions(+), 45 deletions(-)
 create mode 100644 gcc/config/default-f.cc
 create mode 100644 gcc/config/i386/i386-f.cc
 create mode 100644 gcc/config/i386/i386-f.h
 create mode 100644 gcc/config/linux-f.cc
 create mode 100644 gcc/fortran/f-target-def.h
 create mode 100644 gcc/fortran/f-target.def
 create mode 100644 gcc/fortran/f-target.h
 create mode 100644 gcc/testsuite/gfortran.dg/pr42954-linux.f90
 create mode 100644 gcc/testsuite/gfortran.dg/pr42954-x86.f90

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 8ecef4ccdc7..dda02937dbc 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -613,6 +613,8 @@ tm_d_file_list=@tm_d_file_list@
 tm_d_include_list=@tm_d_include_list@
 tm_rust_file_list=@tm_rust_file_list@
 tm_rust_include_list=@tm_rust_include_list@
+tm_f_file_list=@tm_f_file_list@
+tm_f_include_list=@tm_f_include_list@
 tm_jit_file_list=@tm_jit_file_list@
 tm_jit_include_list=@tm_jit_include_list@
 build_xm_file_list=@build_xm_file_list@
@@ -922,6 +924,7 @@ TCONFIG_H = tconfig.h $(xm_file_list)
 TM_P_H    = tm_p.h    $(tm_p_file_list) $(TREE_H)
 TM_D_H    = tm_d.h    $(tm_d_file_list)
 TM_RUST_H = tm_rust.h $(tm_rust_file_list)
+TM_F_H    = tm_f.h    $(tm_f_file_list)
 TM_JIT_H  = tm_jit.h    $(tm_jit_file_list)
 GTM_H     = tm.h      $(tm_file_list) insn-constants.h
 TM_H      = $(GTM_H) insn-flags.h $(OPTIONS_H)
@@ -983,12 +986,14 @@ C_TARGET_DEF = c-family/c-target.def target-hooks-macros.h
 COMMON_TARGET_DEF = common/common-target.def target-hooks-macros.h
 D_TARGET_DEF = d/d-target.def target-hooks-macros.h
 RUST_TARGET_DEF = rust/rust-target.def target-hooks-macros.h
+F_TARGET_DEF = fortran/f-target.def target-hooks-macros.h
 JIT_TARGET_DEF = jit/jit-target.def target-hooks-macros.h
 TARGET_H = $(TM_H) target.h $(TARGET_DEF) insn-modes.h insn-codes.h
 C_TARGET_H = c-family/c-target.h $(C_TARGET_DEF)
 COMMON_TARGET_H = common/common-target.h $(INPUT_H) $(COMMON_TARGET_DEF)
 D_TARGET_H = d/d-target.h $(D_TARGET_DEF)
 RUST_TARGET_H = rust/rust-target.h $(RUST_TARGET_DEF)
+F_TARGET_H = fortran/f-target.h $(F_TARGET_DEF)
 JIT_TARGET_H = jit/jit-target.h $(JIT_TARGET_DEF)
 MACHMODE_H = machmode.h mode-classes.def
 HOOKS_H = hooks.h
@@ -2137,6 +2142,7 @@ tm.h: cs-tm.h ; @true
 tm_p.h: cs-tm_p.h ; @true
 tm_d.h: cs-tm_d.h ; @true
 tm_rust.h: cs-tm_rust.h ; @true
+tm_f.h: cs-tm_f.h ; @true
 tm_jit.h: cs-tm_jit.h ; @true
 
 cs-config.h: Makefile
@@ -2177,6 +2183,11 @@ cs-tm_rust.h: Makefile
 	HEADERS="$(tm_rust_include_list)" DEFINES="" \
 	$(SHELL) $(srcdir)/mkconfig.sh tm_rust.h
 
+cs-tm_f.h: Makefile
+	TARGET_CPU_DEFAULT="" \
+	HEADERS="$(tm_f_include_list)" DEFINES="" \
+	$(SHELL) $(srcdir)/mkconfig.sh tm_f.h
+
 cs-tm_jit.h: Makefile
 	TARGET_CPU_DEFAULT="" \
 	HEADERS="$(tm_jit_include_list)" DEFINES="" \
@@ -2655,6 +2666,12 @@ default-rust.o: config/default-rust.cc
 	$(COMPILE) $<
 	$(POSTCOMPILE)
 
+# Files used by the Fortran language front end.
+
+default-f.o: config/default-f.cc
+	$(COMPILE) $<
+	$(POSTCOMPILE)
+
 # Language-independent files.
 
 DRIVER_DEFINES = \
@@ -3001,6 +3018,15 @@ s-rust-target-hooks-def-h: build/genhooks$(build_exeext)
 					     rust/rust-target-hooks-def.h
 	$(STAMP) s-rust-target-hooks-def-h
 
+fortran/f-target-hooks-def.h: s-f-target-hooks-def-h; @true
+
+s-f-target-hooks-def-h: build/genhooks$(build_exeext)
+	$(RUN_GEN) build/genhooks$(build_exeext) "Fortran Target Hook" \
+					     > tmp-f-target-hooks-def.h
+	$(SHELL) $(srcdir)/../move-if-change tmp-f-target-hooks-def.h \
+					     fortran/f-target-hooks-def.h
+	$(STAMP) s-f-target-hooks-def-h
+
 jit/jit-target-hooks-def.h: s-jit-target-hooks-def-h; @true
 
 s-jit-target-hooks-def-h: build/genhooks$(build_exeext)
@@ -3035,6 +3061,7 @@ s-tm-texi: build/genhooks$(build_exeext) $(srcdir)/doc/tm.texi.in
 	    || test $(srcdir)/doc/tm.texi -nt $(srcdir)/common/common-target.def \
 	    || test $(srcdir)/doc/tm.texi -nt $(srcdir)/d/d-target.def \
 	    || test $(srcdir)/doc/tm.texi -nt $(srcdir)/rust/rust-target.def \
+	    || test $(srcdir)/doc/tm.texi -nt $(srcdir)/fortran/f-target.def \
 	  ); then \
 	  echo >&2 ; \
 	  echo You should edit $(srcdir)/doc/tm.texi.in rather than $(srcdir)/doc/tm.texi . >&2 ; \
@@ -3218,6 +3245,7 @@ generated_files = config.h tm.h $(TM_P_H) $(TM_D_H) $(TM_JIT_H) $(TM_H) \
        gimple-match-auto.h generic-match-auto.h \
        c-family/c-target-hooks-def.h d/d-target-hooks-def.h \
        $(TM_RUST_H) rust/rust-target-hooks-def.h \
+       $(TM_F_H) fortran/f-target-hooks-def.h \
        case-cfn-macros.h \
        jit/jit-target-hooks-def.h case-cfn-macros.h \
        cfn-operators.pd omp-device-properties.h
@@ -3353,7 +3381,8 @@ build/genrecog.o : genrecog.cc $(RTL_BASE_H) $(BCONFIG_H) $(SYSTEM_H)	\
   $(CORETYPES_H) $(GTM_H) errors.h $(READ_MD_H) $(GENSUPPORT_H)		\
   $(HASH_TABLE_H) inchash.h
 build/genhooks.o : genhooks.cc $(TARGET_DEF) $(C_TARGET_DEF)		\
-  $(COMMON_TARGET_DEF) $(D_TARGET_DEF) $(RUST_TARGET_DEF) $(JIT_TARGET_DEF) \
+  $(COMMON_TARGET_DEF) $(D_TARGET_DEF) $(RUST_TARGET_DEF)		\
+  $(F_TARGET_DEF) $(JIT_TARGET_DEF)					\
   $(BCONFIG_H) $(SYSTEM_H) errors.h
 build/genmddump.o : genmddump.cc $(RTL_BASE_H) $(BCONFIG_H) $(SYSTEM_H)	\
   $(CORETYPES_H) $(GTM_H) errors.h $(READ_MD_H) $(GENSUPPORT_H)
diff --git a/gcc/config.gcc b/gcc/config.gcc
index 8fe99616f82..7214670b1d2 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -216,6 +216,9 @@
 #  target_has_targetrustm	Set to yes or no depending on whether the target
 #			has its own definition of targetrustm.
 #
+#  target_has_targetfm	Set to yes or no depending on whether the target
+#			has its own definition of targetfm.
+#
 #  target_has_targetjitm	Set to yes or no depending on whether the target
 #			has its own definition of targetjitm.
 
@@ -241,6 +244,7 @@ target_has_targetcm=no
 target_has_targetm_common=yes
 target_has_targetdm=no
 target_has_targetrustm=no
+target_has_targetfm=no
 target_has_targetjitm=no
 tm_defines=
 xm_defines=
@@ -642,6 +646,16 @@ then
 	rust_target_objs="${rust_target_objs} ${cpu_type}-rust.o"
 fi
 
+tm_f_file=
+if test -f ${srcdir}/config/${cpu_type}/${cpu_type}-f.h
+then
+	tm_f_file="${cpu_type}/${cpu_type}-f.h"
+fi
+if test -f ${srcdir}/config/${cpu_type}/${cpu_type}-f.cc
+then
+	fortran_target_objs="${fortran_target_objs} ${cpu_type}-f.o"
+fi
+
 tm_jit_file=
 if test -f ${srcdir}/config/${cpu_type}/${cpu_type}-jit.h
 then
@@ -1009,6 +1023,8 @@ case ${target} in
       target_has_targetdm=yes
       rust_target_objs="${rust_target_objs} linux-rust.o"
       target_has_targetrustm=yes
+      fortran_target_objs="${fortran_target_objs} linux-f.o"
+      target_has_targetfm=yes
       ;;
     *-*-kfreebsd*-gnu)
       d_target_objs="${d_target_objs} kfreebsd-d.o"
@@ -3791,6 +3807,10 @@ if [ "$target_has_targetrustm" = "no" ]; then
   rust_target_objs="$rust_target_objs default-rust.o"
 fi
 
+if [ "$target_has_targetfm" = "no" ]; then
+  fortran_target_objs="$fortran_target_objs default-f.o"
+fi
+
 if [ "$target_has_targetjitm" = "no" ]; then
   jit_target_objs="$jit_target_objs default-jit.o"
 fi
diff --git a/gcc/config/default-f.cc b/gcc/config/default-f.cc
new file mode 100644
index 00000000000..9968fbbe513
--- /dev/null
+++ b/gcc/config/default-f.cc
@@ -0,0 +1,28 @@
+/* Default Fortran target hook initializer.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+/* Do not include tm.h or tm_p.h here; definitions needed by the target
+   architecture to initialize targetfm should instead be added to tm_f.h.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm_f.h"
+#include "fortran/f-target.h"
+#include "fortran/f-target-def.h"
+
+struct gcc_targetfm targetfm = TARGETFM_INITIALIZER;
diff --git a/gcc/config/i386/i386-f.cc b/gcc/config/i386/i386-f.cc
new file mode 100644
index 00000000000..1476a4e37a6
--- /dev/null
+++ b/gcc/config/i386/i386-f.cc
@@ -0,0 +1,78 @@
+/* x86 support needed only by the Fortran front end.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#define IN_TARGET_CODE 1
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "cpplib.h"
+#include "tm_f.h"
+#include "memmodel.h"
+#include "tm_p.h"
+#include "fortran/f-target.h"
+
+/* Provide the x86 portion of TARGET_F_CPP_BUILTINS.  Mirrors the
+   architecture-identification and float-size portion of
+   ix86_target_macros in gcc/config/i386/i386-c.cc; ISA feature macros
+   (__SSE__, __AVX__, ...) and arch / tune macros (__haswell__,
+   __tune_*__) are intentionally out of scope and remain a follow-up
+   exercise.  Bare-namespace macros ("i386" without underscores) are
+   never emitted because they would clash with valid Fortran
+   identifiers.  */
+
+void
+ix86_f_cpu_cpp_builtins (cpp_reader *pfile)
+{
+  if (TARGET_64BIT)
+    {
+      cpp_assert (pfile, "cpu=x86_64");
+      cpp_assert (pfile, "machine=x86_64");
+      cpp_define (pfile, "__amd64");
+      cpp_define (pfile, "__amd64__");
+      cpp_define (pfile, "__x86_64");
+      cpp_define (pfile, "__x86_64__");
+      if (TARGET_X32)
+	{
+	  cpp_define (pfile, "_ILP32");
+	  cpp_define (pfile, "__ILP32__");
+	}
+    }
+  else
+    {
+      cpp_assert (pfile, "cpu=i386");
+      cpp_assert (pfile, "machine=i386");
+      cpp_define (pfile, "__i386");
+      cpp_define (pfile, "__i386__");
+      cpp_define (pfile, "_ILP32");
+      cpp_define (pfile, "__ILP32__");
+    }
+
+  if (!TARGET_80387)
+    cpp_define (pfile, "_SOFT_FLOAT");
+
+  if (TARGET_LONG_DOUBLE_64)
+    cpp_define (pfile, "__LONG_DOUBLE_64__");
+
+  if (TARGET_LONG_DOUBLE_128)
+    cpp_define (pfile, "__LONG_DOUBLE_128__");
+
+  cpp_define_formatted (pfile, "__SIZEOF_FLOAT80__=%d",
+			GET_MODE_SIZE (XFmode));
+  cpp_define (pfile, "__SIZEOF_FLOAT128__=16");
+}
diff --git a/gcc/config/i386/i386-f.h b/gcc/config/i386/i386-f.h
new file mode 100644
index 00000000000..a87aff058df
--- /dev/null
+++ b/gcc/config/i386/i386-f.h
@@ -0,0 +1,25 @@
+/* Subroutines for the Fortran front end on the x86 architecture.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_I386_F_H
+#define GCC_I386_F_H
+
+extern void ix86_f_cpu_cpp_builtins (cpp_reader *);
+
+#define TARGET_F_CPU_CPP_BUILTINS ix86_f_cpu_cpp_builtins
+
+#endif /* GCC_I386_F_H  */
diff --git a/gcc/config/i386/t-i386 b/gcc/config/i386/t-i386
index ae0fb8ed474..f231ad14841 100644
--- a/gcc/config/i386/t-i386
+++ b/gcc/config/i386/t-i386
@@ -50,6 +50,10 @@ i386-rust.o: $(srcdir)/config/i386/i386-rust.cc
 	$(COMPILE) $<
 	$(POSTCOMPILE)
 
+i386-f.o: $(srcdir)/config/i386/i386-f.cc
+	$(COMPILE) $<
+	$(POSTCOMPILE)
+
 i386-jit.o: $(srcdir)/config/i386/i386-jit.cc
 	$(COMPILE) $<
 	$(POSTCOMPILE)
diff --git a/gcc/config/linux-f.cc b/gcc/config/linux-f.cc
new file mode 100644
index 00000000000..190d33e9a47
--- /dev/null
+++ b/gcc/config/linux-f.cc
@@ -0,0 +1,56 @@
+/* Linux support needed only by the Fortran front end.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "cpplib.h"
+#include "tm_f.h"
+#include "fortran/f-target.h"
+#include "fortran/f-target-def.h"
+
+#ifndef TARGET_F_CPU_CPP_BUILTINS
+#define TARGET_F_CPU_CPP_BUILTINS(PFILE) ((void) (PFILE))
+#endif
+
+/* Implement TARGET_F_CPP_BUILTINS for Linux targets.  This intentionally
+   covers only target-identity macros; option-dependent CPU feature macros
+   can be added by target maintainers in follow-up patches.  */
+
+static void
+linux_f_cpp_builtins (cpp_reader *pfile)
+{
+  TARGET_F_CPU_CPP_BUILTINS (pfile);
+
+  if (OPTION_GLIBC)
+    cpp_define (pfile, "__gnu_linux__");
+  cpp_define (pfile, "__linux__");
+  cpp_define (pfile, "__linux");
+  cpp_define (pfile, "__unix__");
+  cpp_define (pfile, "__unix");
+  cpp_assert (pfile, "system=linux");
+  cpp_assert (pfile, "system=unix");
+  cpp_assert (pfile, "system=posix");
+
+  cpp_define (pfile, "__ELF__");
+}
+
+#undef TARGET_F_CPP_BUILTINS
+#define TARGET_F_CPP_BUILTINS linux_f_cpp_builtins
+
+struct gcc_targetfm targetfm = TARGETFM_INITIALIZER;
diff --git a/gcc/config/t-linux b/gcc/config/t-linux
index 238f1f074ce..b639b78b41f 100644
--- a/gcc/config/t-linux
+++ b/gcc/config/t-linux
@@ -27,3 +27,7 @@ linux-d.o: $(srcdir)/config/linux-d.cc
 linux-rust.o: $(srcdir)/config/linux-rust.cc
 	  $(COMPILE) $<
 	  $(POSTCOMPILE)
+
+linux-f.o: $(srcdir)/config/linux-f.cc
+	  $(COMPILE) $<
+	  $(POSTCOMPILE)
diff --git a/gcc/configure b/gcc/configure
index ef780a23c2f..402a68100af 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -662,6 +662,8 @@ xm_include_list
 xm_file_list
 tm_jit_include_list
 tm_jit_file_list
+tm_f_include_list
+tm_f_file_list
 tm_rust_include_list
 tm_rust_file_list
 tm_d_include_list
@@ -15205,6 +15207,17 @@ for f in $tm_rust_file; do
   esac
 done
 
+tm_f_file_list=
+tm_f_include_list=
+for f in $tm_f_file; do
+  case $f in
+    * )
+       tm_f_file_list="${tm_f_file_list} \$(srcdir)/config/$f"
+       tm_f_include_list="${tm_f_include_list} config/$f"
+       ;;
+  esac
+done
+
 tm_jit_file_list=
 tm_jit_include_list=
 for f in $tm_jit_file; do
@@ -21975,7 +21988,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 21978 "configure"
+#line 21991 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -22081,7 +22094,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 22084 "configure"
+#line 22097 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -34359,6 +34372,8 @@ fi
 
 
 
+
+
 
 
 
diff --git a/gcc/configure.ac b/gcc/configure.ac
index cdf2997cb5f..85d6eef08f0 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -2492,6 +2492,17 @@ for f in $tm_rust_file; do
   esac
 done
 
+tm_f_file_list=
+tm_f_include_list=
+for f in $tm_f_file; do
+  case $f in
+    * )
+       tm_f_file_list="${tm_f_file_list} \$(srcdir)/config/$f"
+       tm_f_include_list="${tm_f_include_list} config/$f"
+       ;;
+  esac
+done
+
 tm_jit_file_list=
 tm_jit_include_list=
 for f in $tm_jit_file; do
@@ -7495,6 +7506,8 @@ AC_SUBST(tm_d_file_list)
 AC_SUBST(tm_d_include_list)
 AC_SUBST(tm_rust_file_list)
 AC_SUBST(tm_rust_include_list)
+AC_SUBST(tm_f_file_list)
+AC_SUBST(tm_f_include_list)
 AC_SUBST(tm_jit_file_list)
 AC_SUBST(tm_jit_include_list)
 AC_SUBST(xm_file_list)
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 2832a447e3e..8661eccc403 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -56,6 +56,7 @@ through the macros defined in the @file{.h} file.
 * C++ ABI::             Controlling C++ ABI changes.
 * D Language and ABI::  Controlling D ABI changes.
 * Rust Language and ABI:: Controlling Rust ABI changes.
+* Fortran Language and ABI:: Controlling Fortran ABI parameters.
 * JIT Language and ABI:: JIT ABI parameters
 * Named Address Spaces:: Adding support for named address spaces
 * Misc::                Everything else.
@@ -11443,6 +11444,19 @@ Similar to @code{TARGET_RUST_CPU_INFO}, but is used for configuration info
 relating to the target operating system.
 @end deftypefn
 
+@node Fortran Language and ABI
+@section Fortran ABI parameters
+@cindex parameters, fortran abi
+
+@deftypefn {Fortran Target Hook} void TARGET_F_CPP_BUILTINS (cpp_reader *@var{pfile})
+Define preprocessor symbols that describe the target for the Fortran
+preprocessor.  Implementations should call @code{cpp_define},
+@code{cpp_assert}, and @code{cpp_define_formatted} (from libcpp) directly
+on @var{pfile}; they must not depend on C-family-only state such as
+@code{parse_in} or @code{flag_iso}.  Bare names such as @code{linux} or
+@code{unix} clash with valid Fortran identifiers and must be omitted.
+@end deftypefn
+
 @node JIT Language and ABI
 @section JIT ABI parameters
 @cindex parameters, jit abi
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 274bb899d0c..c8c20b97b54 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -56,6 +56,7 @@ through the macros defined in the @file{.h} file.
 * C++ ABI::             Controlling C++ ABI changes.
 * D Language and ABI::  Controlling D ABI changes.
 * Rust Language and ABI:: Controlling Rust ABI changes.
+* Fortran Language and ABI:: Controlling Fortran ABI parameters.
 * JIT Language and ABI:: JIT ABI parameters
 * Named Address Spaces:: Adding support for named address spaces
 * Misc::                Everything else.
@@ -7330,6 +7331,12 @@ floating-point support; they are not included in this mechanism.
 
 @hook TARGET_RUST_OS_INFO
 
+@node Fortran Language and ABI
+@section Fortran ABI parameters
+@cindex parameters, fortran abi
+
+@hook TARGET_F_CPP_BUILTINS
+
 @node JIT Language and ABI
 @section JIT ABI parameters
 @cindex parameters, jit abi
diff --git a/gcc/fortran/cpp.cc b/gcc/fortran/cpp.cc
index 6b5f136e4f3..f2646d37d99 100644
--- a/gcc/fortran/cpp.cc
+++ b/gcc/fortran/cpp.cc
@@ -35,23 +35,13 @@ along with GCC; see the file COPYING3.  If not see
 #include "incpath.h"
 #include "cppbuiltin.h"
 #include "mkdeps.h"
+#include "tm_f.h"
+#include "fortran/f-target.h"
 
 #ifndef TARGET_SYSTEM_ROOT
 # define TARGET_SYSTEM_ROOT NULL
 #endif
 
-#ifndef TARGET_CPU_CPP_BUILTINS
-# define TARGET_CPU_CPP_BUILTINS()
-#endif
-
-#ifndef TARGET_OS_CPP_BUILTINS
-# define TARGET_OS_CPP_BUILTINS()
-#endif
-
-#ifndef TARGET_OBJFMT_CPP_BUILTINS
-# define TARGET_OBJFMT_CPP_BUILTINS()
-#endif
-
 
 /* Holds switches parsed by gfc_cpp_handle_option (), but whose
    handling is deferred to gfc_cpp_init ().  */
@@ -177,33 +167,10 @@ cpp_define_builtins (cpp_reader *pfile)
   if (flag_openmp)
     cpp_define (pfile, "_OPENMP=202111");
 
-  /* The defines below are necessary for the TARGET_* macros.
-
-     FIXME:  Note that builtin_define_std() actually is a function
-     in c-cppbuiltin.cc which uses flags undefined for Fortran.
-     Let's skip this for now. If needed, one needs to look into it
-     once more.  */
-
-# define builtin_define(TXT) cpp_define (pfile, TXT)
-# define builtin_define_std(TXT)
-# define builtin_assert(TXT) cpp_assert (pfile, TXT)
-
-  /* FIXME: Pandora's Box
-    Using the macros below results in multiple breakages:
-     - mingw will fail to compile this file as dependent macros
-       assume to be used in c-cppbuiltin.cc only. Further, they use
-       flags only valid/defined in C (same as noted above).
-       [config/i386/mingw32.h, config/i386/cygming.h]
-     - other platforms (not as popular) break similarly
-       [grep for 'builtin_define_with_int_value' in gcc/config/]
-
-  TARGET_CPU_CPP_BUILTINS ();
-  TARGET_OS_CPP_BUILTINS ();
-  TARGET_OBJFMT_CPP_BUILTINS (); */
-
-#undef builtin_define
-#undef builtin_define_std
-#undef builtin_assert
+  /* Provide target-specific cpp macros via a per-target hook.  The hook
+     implementation calls cpp_define / cpp_assert directly and must not
+     depend on C-family-only state such as parse_in or flag_iso.  */
+  targetfm.f_cpp_builtins (pfile);
 }
 
 bool
diff --git a/gcc/fortran/f-target-def.h b/gcc/fortran/f-target-def.h
new file mode 100644
index 00000000000..b1747927e9e
--- /dev/null
+++ b/gcc/fortran/f-target-def.h
@@ -0,0 +1,20 @@
+/* f-target-def.h -- Default initializers for Fortran target hooks.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by the
+   Free Software Foundation; either version 3, or (at your option) any
+   later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "fortran/f-target-hooks-def.h"
+#include "tree.h"
+#include "hooks.h"
diff --git a/gcc/fortran/f-target.def b/gcc/fortran/f-target.def
new file mode 100644
index 00000000000..a9d86607f10
--- /dev/null
+++ b/gcc/fortran/f-target.def
@@ -0,0 +1,44 @@
+/* f-target.def -- Target hook definitions for the Fortran front end.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by the
+   Free Software Foundation; either version 3, or (at your option) any
+   later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+/* See target-hooks-macros.h for details of macros that should be
+   provided by the including file, and how to use them here.  */
+
+#include "target-hooks-macros.h"
+
+#undef HOOK_TYPE
+#define HOOK_TYPE "Fortran Target Hook"
+
+HOOK_VECTOR (TARGETFM_INITIALIZER, gcc_targetfm)
+
+#undef HOOK_PREFIX
+#define HOOK_PREFIX "TARGET_"
+
+/* Target-specific preprocessor builtins.  */
+DEFHOOK
+(f_cpp_builtins,
+ "Define preprocessor symbols that describe the target for the Fortran\n\
+preprocessor.  Implementations should call @code{cpp_define},\n\
+@code{cpp_assert}, and @code{cpp_define_formatted} (from libcpp) directly\n\
+on @var{pfile}; they must not depend on C-family-only state such as\n\
+@code{parse_in} or @code{flag_iso}.  Bare names such as @code{linux} or\n\
+@code{unix} clash with valid Fortran identifiers and must be omitted.",
+ void, (cpp_reader *pfile),
+ hook_void_cpp_reader)
+
+/* Close the 'struct gcc_targetfm' definition.  */
+HOOK_VECTOR_END (C90_EMPTY_HACK)
diff --git a/gcc/fortran/f-target.h b/gcc/fortran/f-target.h
new file mode 100644
index 00000000000..339f614c488
--- /dev/null
+++ b/gcc/fortran/f-target.h
@@ -0,0 +1,32 @@
+/* f-target.h -- Data structure definitions for target-specific Fortran
+   behavior.
+   Copyright (C) 2026 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by the
+   Free Software Foundation; either version 3, or (at your option) any
+   later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_F_TARGET_H
+#define GCC_F_TARGET_H
+
+#define DEFHOOKPOD(NAME, DOC, TYPE, INIT) TYPE NAME;
+#define DEFHOOK(NAME, DOC, TYPE, PARAMS, INIT) TYPE (* NAME) PARAMS;
+#define DEFHOOK_UNDOC DEFHOOK
+#define HOOKSTRUCT(FRAGMENT) FRAGMENT
+
+#include "f-target.def"
+
+/* Each target can provide their own.  */
+extern struct gcc_targetfm targetfm;
+
+#endif /* GCC_F_TARGET_H  */
diff --git a/gcc/genhooks.cc b/gcc/genhooks.cc
index 42dbace771f..cadd6dd3e9e 100644
--- a/gcc/genhooks.cc
+++ b/gcc/genhooks.cc
@@ -36,6 +36,7 @@ static struct hook_desc hook_array[] = {
 #include "common/common-target.def"
 #include "d/d-target.def"
 #include "rust/rust-target.def"
+#include "fortran/f-target.def"
 #include "jit/jit-target.def"
 #undef DEFHOOK
 };
diff --git a/gcc/hooks.cc b/gcc/hooks.cc
index 2b47fd3e50f..f75c7dc1bad 100644
--- a/gcc/hooks.cc
+++ b/gcc/hooks.cc
@@ -306,6 +306,11 @@ hook_void_constcharptr (const char *)
 {
 }
 
+void
+hook_void_cpp_reader (cpp_reader *)
+{
+}
+
 void
 hook_void_tree_treeptr (tree, tree *)
 {
diff --git a/gcc/hooks.h b/gcc/hooks.h
index 1ad4abb5500..2a45b3f8d91 100644
--- a/gcc/hooks.h
+++ b/gcc/hooks.h
@@ -82,6 +82,7 @@ extern bool hook_bool_wint_wint_uint_bool_true (const widest_int &,
 
 extern void hook_void_void (void);
 extern void hook_void_constcharptr (const char *);
+extern void hook_void_cpp_reader (cpp_reader *);
 extern void hook_void_rtx_insn_int (rtx_insn *, int);
 extern void hook_void_FILEptr_constcharptr (FILE *, const char *);
 extern void hook_void_FILEptr_constcharptr_const_tree (FILE *, const char *,
diff --git a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90 b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
index 0e0ab518010..115195e1194 100644
--- a/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
+++ b/gcc/testsuite/gfortran.dg/gomp/declare-variant-10.f90
@@ -64,9 +64,6 @@ contains
     call f18 ()	  ! { dg-final { scan-tree-dump-times "f18 \\\(\\\);" 1 "gimple" } } */
   end subroutine
 
-#if defined(__i386__) || defined(__x86_64__)
-  __attribute__((target ("avx512f,avx512bw")))
-#endif
   subroutine test2 ()
     !$omp target
       call f04 () ! { dg-final { scan-tree-dump-times "f03 \\\(\\\);" 1 "gimple" { target { { i?86-*-* x86_64-*-* } && { ! ilp32 } } } } }
diff --git a/gcc/testsuite/gfortran.dg/pr42954-linux.f90 b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
new file mode 100644
index 00000000000..20a67f1ea5b
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr42954-linux.f90
@@ -0,0 +1,33 @@
+! { dg-do preprocess { target *-*-linux* } }
+! { dg-options "-cpp" }
+!
+! PR fortran/42954 - target macros missing in gfortran -cpp
+
+#ifndef __linux__
+# error __linux__ not defined
+#endif
+
+#ifndef __linux
+# error __linux not defined
+#endif
+
+#ifndef __unix__
+# error __unix__ not defined
+#endif
+
+#ifndef __unix
+# error __unix not defined
+#endif
+
+#ifdef linux
+# error bare linux should not be defined
+#endif
+
+#ifdef unix
+# error bare unix should not be defined
+#endif
+
+#ifndef __ELF__
+# error __ELF__ not defined
+#endif
+end
diff --git a/gcc/testsuite/gfortran.dg/pr42954-x86.f90 b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
new file mode 100644
index 00000000000..07788718286
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr42954-x86.f90
@@ -0,0 +1,11 @@
+! { dg-do preprocess { target { i?86-*-* x86_64-*-* } } }
+! { dg-options "-cpp" }
+!
+! PR fortran/42954 - target macros missing in gfortran -cpp
+
+#if !defined(__i386__) && !defined(__i386) \
+    && !defined(__x86_64__) && !defined(__x86_64) \
+    && !defined(__amd64__) && !defined(__amd64)
+# error x86 target macros not defined
+#endif
+end
-- 
2.54.0
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